CN1433100A

CN1433100A - Fuel cell activating method

Info

Publication number: CN1433100A
Application number: CN02147389A
Authority: CN
Inventors: 安本荣一; 行天久朗; 羽藤一仁; 西田和史; 神原辉寿
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1998-06-01
Filing date: 1999-06-01
Publication date: 2003-07-30
Anticipated expiration: 2019-06-01
Also published as: CN1238922C; EP1981112A3; CN1237804A; EP1981112A2; EP0961334A2; CN1113420C; EP0961334A3; US6187464B1

Abstract

The present invention disclosed a method which comprises the step (a) of enhancing the catalytic activity of said electrode and the step (b) of giving a wetting condition to said polymer electrolyte. The method for activating a polymer electrolyte type fuel cell comprising a unit cell which is configured by including a proton conductive polymer electrolyte, an electrode layer having a catalytic activity arranged on the both faces of said polymer electrolyte membrane and a gas-supplying path is disclosed. According to the present invention, it is possible to readily activate the fuel cell and to cause the same to demonstrate a high cell performance.

Description

Activation method for fuel cell

The present application is a divisional application of chinese patent application having an application date of 1/6/1999, an application number of CN99107155.7, entitled "method for activating fuel cell".

Technical Field

The present invention relates to a fuel cell, and more particularly to a method for activating a solid polymer electrolyte fuel cell.

Background

In recent years, environmental awareness has been increasing, and among them, in the field of batteries, development of solid polymer electrolyte fuel cells (hereinafter referred to as "PEFC") has been actively carried out. Such a fuel cell is currently put to practical use, but its performance as a battery is not fully exhibited for various reasons.

A conventional PEFC is composed of a proton conductive polymer electrolyte membrane, positive and negative electrodes, a gasket located around the electrodes, a carbon black or metal bipolar plate, and a cooling plate. The constituent material of the electrode catalyst layer that contributes to the battery reaction is a mixture of a noble metal catalyst-carrying carbon black powder and the same material as the electrolyte material, and a mixture in which a fluorocarbon-based water-repellent material or the like is added as necessary is a commonly used constituent material. The electrode is formed by bonding the electrode catalyst layer and the gas diffusion layer. The electrode having the above-described structure is combined with a polymer film as an electrolyte to form a battery. When pure hydrogen is used as the fuel, the same materials can be used as the constituent materials of the negative electrode and the positive electrode.

(1) Problems caused by fuel

Generally, city gas or gas in which methanol is reformed is used as fuel for a fuel cell. However, in the case of the PEFC, a platinum catalyst is generally used for the fuel electrode, and since a slight amount of carbon monoxide is contained in the fuel gas, the platinum catalyst is poisoned, and the catalytic activity is lowered, thereby causing a problem that the cell performance is greatly lowered.

In order to avoid the above phenomenon, various methods have been proposed. One method is a hydrogen separation method in which CO in the fuel gas is removed by a Pd membrane before the fuel gas is fed to the PEFC. This method is a method of selectively allowing only hydrogen gas to permeate through a hydrogen separation membrane by applying a predetermined pressure to one side of the membrane. Since this method does not allow gas other than hydrogen to permeate therethrough, pure hydrogen can be supplied only to the PEFC. The method is practically applied to equipment for semiconductor production and the like, and only a part of the method has been developed as PEFC.

As another method for reducing the CO concentration in the fuel gas, a so-called CO conversion method is proposed. The methanol or the city gas is modified by water vapor, and CO is removed from the modified gas by a CO conversion catalyst ( ). The CO concentration in the gas can be reduced to 0.4-1.5% by the method. When the CO is reduced to the above level, it can be used as a fuel for a phosphoric acid fuel cell using a Pt electrode catalyst as well. However, in order to prevent the platinum catalyst poisoning of the fuel electrode used for the PEFC, the CO concentration must be reduced to at least a level of several ppm, but the above CO conversion method is not sufficient.

Therefore, a method has been proposed in which oxygen (air) is introduced again into the gas after CO conversion, and CO is further oxidized and removed at 200 to 300 ℃ by using an oxidation catalyst. The oxidation catalyst used here is an alumina catalyst or the like carrying a noble metal. However, it is very difficult to selectively and completely oxidize a trace amount of CO in hydrogen.

In addition, a method of directly mixing air into fuel gas and oxidizing and removing CO with a fuel electrode has also been proposed. This method is preferable from the viewpoint of downsizing because it does not require a complicated gas treatment apparatus, but it is difficult to completely remove CO.

Further, various studies have been made on the use of an alloy catalyst having high resistance to CO poisoning by changing the electrode catalyst, but the performance is still insufficient in the present situation, and it is difficult to develop a catalyst for an electrode which does not adsorb CO at all.

Furthermore, even when a CO conversion method, a CO oxidation method, or a method of mixing air into fuel gas is used, it is difficult to sufficiently reduce the CO concentration to a level that can be used as a PEFC fuel. In particular, at the time of starting the fuel cell, there is a risk that a large amount of CO is contained in the fuel gas, and it is necessary to introduce the CO into the fuel cell after stabilizing the performance for a sufficient time, or to separately provide a hydrogen cylinder for starting. In addition, even during normal operation, since CO gradually accumulates in the fuel electrode, the battery performance is degraded. When the cell performance is lowered, the cell performance is maintained and does not recover, and it is necessary to temporarily stop the operation of the fuel cell, introduce a large amount of air, oxidize and remove CO, or exchange thefuel cell with the electrode.

As is apparent from the above, the conventional hydrogen separation method using a metal hydride membrane such as a Pd membrane can obtain high-purity hydrogen, and is therefore most suitable as a PEFC fuel. However, the Pd membrane is very expensive, and there is a problem in production cost. Further, since hydrogen gas is basically obtained by utilizing a pressure difference, there is a problem that the apparatus structure is complicated.

(2) Problems caused by the water repellency of the polymer electrolyte membrane

On the other hand, the polymer electrolyte is generally used with-CF₂-as main chain, with sulfonic acid group (-SO)₃H) A material having a side chain having a terminal functional group, and having proton-conducting electrolyte properties when it contains water. Therefore, when the battery is in operation, the electrolyte generally needs to be in a water-containing state, and the electrolyte in the water-containing state is strongly acidic. Therefore, the material of the portion in direct contact with the electrolyte is required to have acid resistance.

Since the electrolyte in a water-containing state has electrolyte properties, it is necessary to supply fuel and air humidified to a temperature dew point of the same extent as the cell operating temperature to the cell at the time of PEFC operation. In particular, the higher the cell operating temperature, the more important humidification control of the supplied gas becomes.

When the PEFC is operated immediately after formation of the PEFC or when the cell left unused for a long time is operated again, it is generally difficult to instantaneously obtain a high-performance cell output even if the temperature of the cell is maintained at a predetermined temperature and the amount of humidification of the supplied gas are controlled to a certain degree. This is because the electrode diffusion layer of the PEFC is subjected to a water repellent treatment, and therefore, it takes a long time to hydrate the initial electrode diffusion layer which is not wetted at all.

Further, sufficient moisture absorption by the same material as the polymer electrolyte contained in the electrode catalyst also requires a long time. Further, even if the temperature of the battery is maintained at a predetermined temperature and the supply gas whose temperature and amount of humidification are controlled to a predetermined level is supplied for a long time, it is not easy to hydrate the electrode diffusion layer in a no-load state. Further, the same material as the polymer electrolyte contained in the electrode catalyst is difficult to absorb moisture, and if power is continuously generated at a high current density, the battery may be forced to generate high-performance battery power originally provided in the battery after several days.

Therefore, conventionally, in order to make the battery generate high-performance power as quickly as possible, activation treatment has been performed such as generating power at a higher current density in pure oxygen, or performing potential limitation so as to maintain the battery voltage in the vicinity of 0V in a state where a large flow rate of supply gas is sufficiently supplied. Even when the above method is used, there is a problem that it takes several hours or more to cause the battery to generate high-performance battery power which is originally provided.

Disclosure of Invention

An object of the present invention is to provide a method for solving the above problems (1) and (2), and more specifically, to provide a method for activating a fuel cell which is excellent in the effect of preventing thedeterioration of the cell performance due to CO or facilitating the recovery of the function, and a method for activating a fuel cell which is improved in the effect of delaying the exertion of the cell performance due to the water resistance of a polymer electrolyte membrane.

In order to solve the above problems, the present invention provides a method for activating a solid polymer electrolyte fuel cell comprising a unit cell having a hydrogen ion conductive polymer electrolyte membrane, electrode layers provided on both sides of the polymer electrolyte membrane and having a catalyst reaction layer, and a gas supply channel, the method comprising the step (a) of increasing the catalyst activity of the catalyst reaction layer and/or the step (b) of imparting wettability to the electrolyte membrane.

The structure of the fuel cell is not particularly limited.

In the step (a), it is preferable that the output voltage of the polymer electrolyte fuel cell is forcibly reduced to increase the catalytic activity of the catalyst reaction layer.

In this case, it is preferable that the output voltage of the unit cell is reduced to 0 to 0.3V. Furthermore, the output voltage may also be stepped down continuously.

In the step (b), it is preferable that the polymer electrolyte fuel cell is immersed in deionized water or weakly acidic water and then boiled.

In addition, in the step (b), it is preferable that deionized water or weakly acidic water having a temperature higher than the operating temperature of the polymer electrolyte fuel cell is injected into the gas supply channel.

In this case, the pressure of the deionized water or weakly acidic water injected into the gas supply passage is preferably 0.1kgf/cm²The above.

In the step (b), it is preferable that the gas supply channel is washed with water vapor, deionized water or weakly acidic water after the ethanol is injected into the gas supply channel.

The weakly acidic water is preferably an aqueous hydrogen peroxide solution.

Further, it is preferable that the ion exchange group of the electrolyte membrane is SO₃H, the weak acidic water is a dilute sulfuric acid aqueous solution.

Preferably, in the step (a), the power generation is performed at an oxygen utilization rate of 50% or more, and then, a voltage is applied to the fuel cell so that the average voltage of the unit cells is maintained at 0.3V or less.

Brief Description of Drawings

Fig. 1 is a configuration diagram of a fuel cell system used in example 1 of the present invention.

Fig. 2 shows the current-voltage characteristics of the fuel cell used in example 1 of the present invention.

Fig. 3 shows the current-voltage characteristics of the fuel cell used in example 1 of the present invention.

Fig. 4 shows the relationship between the operating time and the voltage of the fuel cell used in example 2 of the present invention.

Detailed Description

The method for activating a PEFC of the present invention is characterized by comprising a step (a) of increasing the catalytic activity of the catalyst reaction layer constituting the PEFC and a step (b) of imparting wettability to the electrolyte membrane.

The aforementioned step (a) can solve the aforementioned problem (1), and theaforementioned step (b) can solve the aforementioned problem (2).

In the step (a), when a fuel gas obtained by reforming a hydrocarbon-based raw material gas and an oxidant gas are introduced into a PEFC to generate a direct current, the output voltage of the cell is forcibly lowered at a proper time to remove carbon monoxide adsorbed in a catalyst reaction portion, thereby recovering the catalyst activity and maintaining the output characteristics of the cell. This step can omit the hydrogen treatment for startup, which has been necessary in the startup process. Further, even if the fuel cell performance is reduced by CO poisoning, CO adsorbed by the catalyst can be easily removed, and the cell performance can be recovered.

In the step (b), the PEFC is boiled in deionized water or weakly acidic water, whereby the battery can be easily made to emit high-performance battery power originally possessed by the battery in a short time. In this case, by boiling in weakly acidic water, impurity ions contained in the same material as the polymer electrolyte contained in the electrolyte membrane and the electrode catalyst layer can be exchanged with protons, and higher performance can be exhibited.

However, it is difficult to boil a large-area multi-layer PEFC in water in view of container capacity, handling difficulty, and the like. Therefore, deionized water or weakly acidic water having a temperature higher than a predetermined cell operating temperature is injected into the gas supply channel of the PEFC, whereby the cell can be easily caused to emit high-performance cell power originally possessed by the cell in a short time. It is more preferable to increase the water pressure at this time to 0.1kgf/cm²Thus, high-performance battery power can be emitted more quickly。

Further, by injecting ethanol into the gas supply channel of the PEFC,the diffusion layer of the electrode can be immediately merged with ethanol. Then, the electrode diffusion layer can be hydrated in a short time by washing with steam, deionized water, or weakly acidic water, so that the battery can emit high-performance battery power which is originally possessed by the battery.

At this time, if ethanol remains on the fuel electrode side, the electrode catalyst oxidizes the alcohol to generate an electrode poisoning substance. Hydration of the electrode diffusion layer on the anode side is more important than the fuel electrode side in order for the cell to emit high-performance cell power that is inherently possessed. Therefore, even if ethanol is injected only on the air side, sufficient effects can be obtained. Further, it is preferable that the oxidizing gas is injected into the fuel electrode side immediately after the activation treatment, and the electrode poisoning material is further oxidized and removed, and then the fuel gas is supplied.

As the polymer electrolyte, for example, -CF is used₂-as main chain, with sulfonic acid group (-SO)₃H) In the case of a material having a side chain having a terminal functional group, it is preferable to use a dilute aqueous sulfuric acid solution as weakly acidic water for activation. The reason for this is that the ion exchange group of the polymer electrolyte is-SO₃Therefore, even if dilute sulfuric acid is injected, sulfate ions do not remain.

For example, formula (1)

Perfluorocarbon sulfonic acids as shown, and the like.

In addition, the deionized water or weakly acidic water injected during the activation process must remove metal ions. The reason for this is that,ion exchange groups of the polyelectrolyte, if metal ions are present, e.g., -SO₃Will combine with metal ions to form-SO₃Me (Me is a metal element), and thus the ion exchange ability is lost. In order to prevent this phenomenon, a hydrogen peroxide aqueous solution composed of pure hydrogen ions is particularly useful as the weakly acidic water to be injected.

Further, the PEFC is caused to generate electricity at an oxygen utilization rate of 50% or more, the positive electrode side of the cell is put in a half-rest state, the average cell voltage is kept at 0.3V or less, and the high-performance cell power originally possessed by the cell can be easily generated in a short time by the water vapor generated by the cell.

The method for activating a fuel cell according to the present invention will be described below with reference to examples, but the present invention is not limited thereto.

Examples 1 to 3

First, the PEFC is constructed by the following method. Platinum particles having an average particle diameter of about 30 angstroms are supported on 25 wt% of acetylene black-based carbon black powder, and used as a catalyst for a reaction electrode. An ethanol suspension in which perfluorocarbon sulfonic acid powder is dispersed is mixed with an isopropyl alcohol solution in which the catalyst powder is dispersed to form a paste. The paste was used as a raw material, and an electrode catalyst layer was formed on one surface of a nonwoven fabric having a thickness of 250 μm by a screen printing method. The amount of platinum contained in the formed reaction electrode was 0.5mg/cm²The amount of perfluorocarbon sulfonic acid is 1.2mg/cm²。

In these electrode plates, the positive electrode and the negative electrode are both of the same configuration, and the formed area is one turn larger than the electrode. Then, as the proton conductive polymer electrolyte, a perfluorocarbon sulfonic acid membrane having athickness of 25 μm was used, and catalyst layers printed on both sides of the central portion of the electrolyte membrane were joined to the electrolyte membrane side by hot pressing to obtain an electrode/electrolyte assembly (MEA).

Subsequently, holes for reaction electrode and gas collection were provided, and a plate-like backing plate was obtained. The electrolyte membrane portion around the MEA electrode was sandwiched by 2 gasket plates, and the reaction electrode portion of the MEA was fitted into the reaction electrode hole in the center portion thereof. Then, 2 bipolar plates each having a non-porous carbon black plate as a base material were sandwiched between the MEA and the gasket plate, and the gas flow paths of the bipolar plates were opposed to each other, thereby constructing a polymer electrolyte fuel cell. As the above plate-like molded body liner plate, a plate obtained by perforating a butyl rubber having a thickness of 250 μm as required can be used.

A heating plate having a gas collecting hole, a current collecting plate, an insulating plate and a base plate are provided on both outer sides of a PEFC, and a bolt, a spring and a nut are used to apply an electrode area of 20kg/cm between the outermost two base plates²The pressure of (b) tightens them to constitute a unit cell (unit cell) of the PEFC. Stacking 50 of the above single cells constitutes a PEFC module.

The temperature of the obtained module was maintained at 75 ℃, hydrogen gas was supplied to one electrode to humidify and warm the module so that the dew point was 73 ℃, and air was supplied to the other electrode to humidify and warm the module so that the dew point was 68 ℃. As a result, in a no-load state where no current is externally output, a battery open-circuit voltage of 0.98V is obtained.

The fuel cell system used in the present embodiment is constructed as shown in fig. 1. In fig. 1, the desulfurized city gas is introduced into a reformer 1 at an S/C (steam to carbon ratio) of 3, and steam reforming and CO conversion are performed. The reformed gas discharged from the reformer 1 is introduced into a CO oxidation removal unit 2 filled with a Pt catalyst to remove O₂the/CO ratio is 1 and is finally introduced into the module 3.

Under normal conditions, the CO concentration in the fuel gas introduced into the module is below 100 ppm. However, the CO concentration in the fuel gas at the time of startup is 1% or more. The operating temperature of the PEFC was 80 ℃, the gas humidification temperature was set at 75 ℃ for the fuel gas, and the oxidizer gas (air) was set at 65 ℃.

First, the fuel cell characteristics when fuel gas was introduced without any treatment after the start of the PEFC were evaluated. Fig. 2 shows the result of comparing the current-voltage characteristics at this time with the case where pure hydrogen gas was introduced. As can be seen from fig. 2, after the start of the PEFC, the battery characteristics significantly deteriorate if no treatment is performed.

Then, the activation method of the present invention was evaluated (example 1). That is, when the PEFC is started, an appropriate resistance is connected between the battery output terminals, and the closed circuit voltage of the battery is reduced to 0.2V within 2 seconds, and then the battery performance is evaluated. Fig. 3 shows the result of comparing the current-voltage characteristics at this time with those in the case where no treatment was performed. As can be seen from fig. 3, temporarily lowering the voltage (short circuit) results in improved battery performance.

This is because the output voltage of the PEFC is forcibly reduced to lower the electrode potential of the MEA to the oxidation potential of CO, thereby oxidizing CO adsorbed on the Pt catalyst.

Next, the battery performance when the time during which the output voltage of the PEFC was forcibly reduced was changed was evaluated (example 2). The output voltage at the time of starting the fuel cell is forcibly reduced to 10V, that is, the cell voltage is maintained at 10V when the single cell is reduced to 0.2V, and the output current of the fuel cell after this step is carried out is 500mA/cm²The cell closed circuit voltage at time is shown in table 1. As is clear from table 1, the battery performance is good when the time for which the battery voltage is forcibly reduced is 10 seconds or less, and the battery performance is deteriorated if the time is longer than 10 seconds.

TABLE 1

Voltage reduction time (seconds)	Voltage of battery (V)
Voltage reduction time (seconds)	Voltage of battery (V)	Pure hydrogen gas	33
0.01	29	Pure hydrogen gas	33
0.01	29	0.5	30
1	31	0.5	30
1	31	5	32
10	33	5	32
10	33	15	31
20	29	15	31

Then, the battery performance when the voltage that forcibly lowers the output voltage of the battery was changed was evaluated (example 3). Table 2 shows that the battery output was 200mA/cm when the lowered voltage was changed with the time for forcibly lowering the battery voltage set at 5 seconds and after the lapse of this step²The closed circuit voltage of the battery. As can be seen from table 2, if the voltage drop of the unit cell is in the range of 0 to 0.3V, the cell voltage shows almost the same performance as that of the case of using pure hydrogen gas, and in addition, the recovery rate of the cell voltage is small and lower by 5V or more than that of the case of pure hydrogen gas.

TABLE 2

Voltage (V) at the time of forcible decrease	Voltage of battery (V)
Voltage (V) at the time of forcible decrease	Voltage of battery (V)	Pure hydrogen gas	36
40	2.5	Pure hydrogen gas	36
40	2.5	30	10
20	30	30	10
20	30	15	34
10	34	15	34
10	34	5	35
2.5	35	5	35
2.5	35	0	35

As can be seen from the above evaluation, there is an effective range in the time and voltage for forcibly lowering the output voltage of the PEFC according to the cell configuration. If the time for forcibly lowering the battery voltage is more than the necessary range, a battery in which the closed-circuit voltage falls below 0V and becomes negative, that is, a polarity-reversed state, appears among the 50 cells connected in series. A relatively effective method for avoiding this is a method in which the entire output voltage is forcibly reduced within a range in which polarity reversal of the unit cells does not occur while monitoring the voltage of each cell.

Example 4

Example 4 of the present invention used the PEFC obtained in example 1. After controlling the CO concentration to be less than 100ppm within 1 hour of starting, the fuel gas is introduced into the fuel cell. Then, at 500mA/cm²The voltage and time relationship at 1000 hours of continuous power generation is shown in FIG. 4.

As can be seen from fig. 4, the voltage is reduced by 10% from the initial stage. Therefore, at this time, an attempt has been made to temporarily reduce the electromotive force of the battery. After the output voltage of the battery is reduced from 47V to 5V within 5 seconds, the voltage is again reduced to 500mA/cm²Power generation is performed. The battery voltage at this time is greatly improved as compared with that before the treatment.

Then, the number of times of processing was changed, and the characteristics after the processing were also evaluated. Table 3 shows the cell voltages after the treatments performed for each number of treatments. As can be seen from table 3, the more times the battery electromotive force is temporarily reduced, the better the effect.

TABLE 3

Number of treatments (times)	Voltage of battery (V)
Number of treatments (times)	Voltage of battery (V)	1	32
2	32	1	32
2	32	5	33
7	33	5	33
7	33	10	33
15	34	10	33
15	34	20	34

As is clear from the above results, by forcibly reducing the cell output voltage of the PEFC temporarily, the problem of poisoning by CO at the time of starting the PEFC, which has been the conventional problem, can be solved, and the fuel gas can be used as it is.

It is also found that even when the performance of the PEFC is reduced by CO during the normal operation, the performance can be restored to approximately the same level as the initial one by temporarily forcibly reducing the cell output voltage.

It is also found that the effect is good when the time for temporarily reducing the battery electromotive force is 10 seconds or less, or the number of times is 2 or more, or the temporarily reduced voltage of the single cell is 0V to 0.3V. The fuel gas used here is reformed city fuel gas, but the use of fuel gas is not particularly limited. Further, an alloy catalyst or the like other than the present invention may be used as an electrode catalyst for a fuel cell.

Example 5 and comparative example 1

A single cell of PEFC was produced in the same manner as in example 1.

The cell was boiled in ion-exchanged distilled water for 1 hour.

Then, the temperature of the cell (PEFC) was maintained at 75 ℃, hydrogen gas was supplied to one electrode to humidify and warm the cell so that the dew point was 73 ℃, and air was supplied to the other electrode to humidify and warm the cell so that the dew point was 68 ℃. Under no load, a battery voltage of 0.98V may be obtained. Further, the fuel utilization rate was 80%, the oxygen utilization rate was 40%, and the current density was 0.3A/cm²The cell was subjected to a continuous power generation test under the conditions of (1). A cell voltage of 0.7V or more can be obtained immediately after power generation. The battery voltage of 0.7V or more is maintained for 5000 hours or more, and the battery voltage does not drop, and power generation can be performed.

For comparison, a power generation test was performed under the same conditions using a single cell having the same structure, but without boiling the cell in ion-exchanged distilled water to obtain a PEFC which was not subjected to activation treatment. As a result, a battery voltage of 0.93V can be obtained only at no load. Further, the fuel utilization rate was 80%, the oxygen utilization rate was 40%, and the current density was 0.3A/cm²The battery is initially inoperable, and if a load is forcibly applied, the starting voltage drops to 0V or less. Therefore, the fuel utilization rate was 70%, the oxygen utilization rate was 20%, and the current density was 0.1A/cm²The power generation test was conducted under the conditions of (1), and it was confirmed that the performance was gradually improved and the load was increased to 0.7A/cm in stages². Repeating the above operation 3 times, and then, returning the gas utilization rate and the like to the previous conditions at 0.3A/cm²The battery voltage of 0.7V or more is obtained under the load, and it takes about 3 days.

This example is an example in which a battery is boiled in ion-exchanged distilled water. The same effect can be obtained if the cell is storedin an aqueous hydrogen peroxide solution having a pH of 5 for 2 hours.

Example 6

The PEFC cells produced in the same manner as in example 5 were stacked in 100 stages. A current collecting plate, an insulating plate and a bottom plate, in which necessary holes for gas collection and cooling water collection are provided, are attached to both outer sides of the laminated cell, and a bolt, a spring and a nut are used to apply a force of 20kg/cm to the electrode area between the two outermost bottom plates²The pressure of which tightens them to form the PEFC assembly.

A 0.01N aqueous solution of sulfuric acid having a temperature of 95 ℃ was injected from two gas injection ports on the positive electrode side and the negative electrode side of the cell for 30 minutes. At this time, the outlet side was contracted to give the injected aqueous solution a value of 0.1kgf/cm²The pressure of (a).

Then, the temperature of the PEFC module was maintained at 75 ℃ by circulation of cooling water, and the PEFC module was lifted to one side electrodeHydrogen gas whose dew point was 73 ℃ by humidification and heating was supplied, and air whose dew point was 68 ℃ by humidification and heating was supplied to the other side. At no load, a battery voltage of 0.98V can be obtained. Further, the fuel utilization rate was 80%, the oxygen utilization rate was 40%, and the current density was 0.3A/cm²The cell was subjected to a continuous power generation test under the conditions of (1). A cell voltage of 0.7V or more can be obtained immediately after power generation. Then adding more than 0.7VThe battery voltage is maintained for 5000 hours or more, and the battery voltage does not drop, and power generation can be performed.

In this example, a 0.01N sulfuric acid aqueous solution at 95 ℃ was injectedfrom two gas injection ports on the positive electrode side and the negative electrode side of a single cell and activated within 30 minutes. The same effect can be obtained if an aqueous hydrogen peroxide solution at 90 ℃ and pH 5 is injected and activated within 1 hour. The same effect can be obtained by injecting deionized water at 95 ℃ over 3 hours.

Example 7

About 100cc of methanol was injected from a gas supply port of a cell (PEFC) produced in the same manner as in example 5, and then washed with ion-exchanged distilled water. Then, the PEFC was maintained at 75 ℃ and air was supplied to the both side electrodes to humidify and warm them to a dew point of 70 ℃ for 1 hour, and then the gas on the fuel electrode side was replaced with nitrogen gas. Then, hydrogen gas having a dew point of 73 ℃ by humidification and warming is supplied to the fuel electrode side, and air having a dew point of 68 ℃ by humidification and warming is supplied to the air electrode side. At no load, a battery voltage of 0.98V can be obtained. Further, the fuel utilization rate was 80%, the oxygen utilization rate was 40%, and the current density was 0.3A/cm²The cell was subjected to a continuous power generation test under the conditions of (1). A cell voltage of 0.7V or more can be obtained immediately after power generation. The battery voltage of 0.7V or more is maintained for 5000 hours or more, and the battery voltage does not drop, and power generation can be performed.

This example is an example in which after methanol injection, the solution is activated by the supplied ion-exchanged distilled water. However, the same effect can be obtained by injecting an aqueous hydrogen peroxide solution having a pH of 5 within 1 hour to activate the solution. The same effect can be obtained also with a dilute aqueous sulfuric acid solution having a pH of 5.

Example 8

The temperature of the single cell (PEFC) produced in the same manner as in example 5 was raised to 75 ℃ without activation treatment. Then, hydrogen gas having a dew point of 73 ℃ by humidification and warming is supplied to the fuel electrode side, and air having a dew point of 68 ℃ by humidification and warming is supplied to the air electrode side. When no load is applied, a battery voltage of 0.93V can be obtained. Then, the gas flow rate was adjusted so that the fuel utilization rate and the oxygen utilization rate were changed to 90% and 60%, respectively, while the cell voltage was decreased to 0.1V, so that the cell was subjected to low potential power generation for 1 hour.

Then, the gas flow rate was adjusted so that the fuel utilization rate and the oxygen utilization rate were changed to 90% and 60%, respectively, at 0.3A/cm²The continuous power generation test was performed at a constant current density of (2). A cell voltage of 0.7V or more can be obtained immediately after power generation. Then the battery voltage of more than 0.7V is kept for more than 5000 hours, and the battery voltage can not be droppedAnd power generation can be performed.

In this example, the voltage applied for activation of the single cell was 0.1V, but when the voltage was higher than 0.3V, the effect was reduced. Further, if the voltage applied to the cell is lower than 0V, the output characteristics of the battery deteriorate if the voltage is applied for a long time. This is because if the applied voltage of the single cell is lower than 0V, a so-called polarity inversion phenomenon of the battery is caused, and the battery reaction part is partially destroyed.

As is apparent from the above-described embodiments, the present invention enables direct introduction of gas at start-up. Even if the performance of the fuel cell is degraded by CO, the electromotiveforce of the cell is temporarily reduced, so that CO adsorbed on the fuel electrode can be easily removed, and the cell performance can be recovered.

As described above, the present invention can easily cause the PEFC to emit high-performance battery power in a short time by boiling the PEFC in deionized water or weakly acidic water. Further, deionized water or weakly acidic water having a temperature higher than a predetermined cell operating temperature is injected into the PEFC gas supply passage, whereby the cell can be easily caused to generate high-performance cell power originally possessed by the cell in a short time. More preferably, the water pressure is increased to 0.1kgf/cm²In the above, high-performance battery power is emitted more quickly.

Further, by injecting ethanol into the PEFC gas supply passage and then washing with steam, deionized water, or weakly acidic water, it is possible to easily cause the cell to emit high-performance battery power originally possessed by the cell in a short time.

Further, by generating power by the PEFC at an oxygen utilization rate of 50% or more, the average voltage of the cell is reduced to a potential of 0.3V or less and kept for 10 seconds or more, and the cell can be easily caused to generate a high-performance cell power originally possessed by the cell in a short time.

Claims

1. A method for activating a solid polymer fuel cell comprising a unit cell having a hydrogen ion conductive polymer electrolyte membrane, electrode layers provided on both sides of the polymer electrolyte membrane and having a catalyst reaction part, and a gas supply channel, wherein the method comprises a step (b) of immersing the solid polymer fuel cell in deionized water or weakly acidic water and boiling the water to inject the deionized water or weakly acidic water having a temperature higher than the operating temperature of the solid polymer fuel cell into the gas supply channel, or injecting ethanol into the gas supply channel, and then washing the gas supply channel with steam, deionized water, or weakly acidic water to impart wettability to the electrolyte membrane.

2. The method for activating a solid polymer fuel cell according to claim 1, wherein the pressure of the deionized water or weakly acidic water injected into the gas supply channel is 0.1kgf/cm²The above.

3. The method for activating a solid polymer fuel cell according to claim 1, wherein the weakly acidic water is an aqueous hydrogen peroxide solution.

4. The method for activating a solid polymer fuel cell according to claim 1, wherein the ion exchange group of the electrolyte membrane is SO₃H, the weak acidic water is a dilute sulfuric acid aqueous solution.